1. Field of the Invention
The present invention relates to a datalink (layer 2) integrated access scheme for providing a communication channel which transmits PPP (Point-to-Point Protocol) packets and PPP related information (such as login prompt, password prompt, etc.), independent of a physical channel, to realize multi-functional access to a computer network.
2. Description of the Background Art
The currently popular scheme for accessing a computer network such as Internet or Intranet from a mobile terminal is a scheme that uses a dial-up through a public network channel to set up a connection to a PPP access server. However, this conventional scheme has been associated with the problem that, when there arises a need to change communication media due to the movement of a mobile terminal during one communication session, for example, it has been either impossible to change communication media while maintaining this communication session, or necessary to rewrite program codes for changing API level in order to change communication media.
As a technique for supporting a free geographic movement by a user or a technique for eliminating dependency on communication media, there are various propositions including Mobile IP, CDPD (Cellular Digital Packet Data), L2-1 call (Seamless Network), one-number service, and Virtual LAN.
The Mobile IP supports the mobility of a mobile terminal by using two types of global IP addresses for the purpose of identifying the terminal itself on a home network of the terminal and a position of the terminal that is registered by a home agent provided on the home network, and updating an IP address for identifying a position of the terminal at a visited site as registered by the home agent whenever the terminal moves. When the terminal wishes to receive a packet destined to it at the visited site, the home agent receives that packet once and transmits it to the IP address of the terminal that is managed by the home agent by using the IP tunnelling, so that it is possible to support the mobility of the terminal and enable media exchange during communication. However, the Mobile IP is associated with the problem that it is only applicable to communication using IP, and there is a need to make changes in the IP protocol stack. In the Mobile IP, there is a need to add a stack on the IP layer in order to utilize the Mobile IP, so that there is a need to make changes in the existing application programs.
The CDPD uses a global IP address for identifying a terminal. In the CDPD network, a MD-IS (Mobile Data Intermediate System) connected with a network to which the terminal is normally connected is called a Home MD-IS and a MD-IS connected with a network to which the moved terminal is connected is called a Serving MD-IS. When the terminal moves, the terminal notifies the Serving MD-IS that it is connected to the network of the Serving MD-IS while requesting the Serving MD-IS to issue a request for position registration to the Home MD-IS. Upon receiving this request from the Serving MD-IS, the Home MD-IS of the terminal makes the position registration of the terminal by mapping the Serving MD-IS that manages the network to which the terminal is currently connected, with respect to the terminal. A packet destined to the terminal always reaches to the Home MD-IS first, and is forwarded to the Serving MD-IS from there according to the registered position registration. Upon receiving this packet, the Serving MD-IS forwards this packet to the terminal so that the terminal can receive the packet no matter where it moves.
The CDPD has a scalability for the movement of the terminal because communication is carried out by CLNP (Connection-Less Network Protocol) between MD-ISs, and in addition, has a higher safety from a viewpoint of security because the communication is carried out through networks dedicated to CDPD rather than through open IP networks such as Internet.
However, the CDPD network only supports the mobility of the terminal and cannot exchange communication media during communication. Moreover, there is a need to allocate global IP addresses statically in order to realize the dial-out service from a server side. In particular, the dial-out service from a server on the intranet which utilizes private IP addresses requires the conversion of the private addresses into global addresses so that it is difficult to realize in the CDPD. Furthermore, media that can utilize the CDPD networks are limited so that it is difficult to deal with new media.
The L2-1 call (Seamless Network) enables communication between terminals of different media by inter-connecting networks of different media and enabling recognition of telephone numbers of different media by the function of networks. Here, the telephone number is used to identify the terminal so that communications can use not just IP but also various other protocols. However, it is difficult to deal with new media because it requires to incorporate a system for recognizing telephone numbers into the network, and no consideration has been given for the dial-out service (a service for sending a packet to a user side terminal by calling up from a provider side) and the media exchange during communication.
In addition, L2TP provides multi-functional access to networks but cannot realize the media exchange during communication and it is impossible to make dial-out connections to many users even when the dial-out service is contemplated.
The one-number service is a service in which a call is terminated at the center once and then connected to media registered to the center in advance by the user. Here, the telephone number is used to identify the user. In this service, the assigned telephone number indicates the geographic condition and the center to be connected is fixed so that a call path may turn out to be wasteful. For example, there can be a case where the center at Tokyo is called up from Osaka and the center at Tokyo calls up another telephone at Osaka. In this service, it is impossible to realize the media exchange during communication.
In the Virtual LAN, the terminal obtains a terminal identifier dependent on access media by sending an identifier dependent on a network protocol to be used that is given to that terminal, such as IP address for example, to a server that manages the position of that terminal, and the terminal itself directly establishes a communication path to the correspondent. In this scheme, the mobility of the terminal is supported, but it is impossible to realize the media exchange during communication. In addition, the set up of the connection to the correspondent is to be attempted by the terminal directly so that the communication path cannot be established when the respective communication media networks are not connected, and consequently it is difficult to deal with new access media.
As described, conventionally, a case where a user makes connection to a computer network such as Internet or Intranet, for example, has been mostly handled by the dial-up connection using company's network or home telephone network. However, there are remarkable advances of radio based communication media such as a portable telephone and PHS (Personal Handy Phone System), and the network access by the dial-up connection using these media is becoming wide spread. In addition, there is a considerable increase in the number of users using notebook PCs so that the support of the mobility of the terminal is becoming an important issue.
Currently, in order to change communication media to be used during communication, it is necessary to terminate a communication session by a communication application used on a computer once, and establish a communication session once again after the change of communication media.
For example, when ftp is executed by setting up a connection to a server by using the PHS first, it is difficult to continue that ftp while changing the medium to be utilized for communication from the PHS to the portable telephone without terminating that ftp session.
In a case where a server tries to set up connections to many users, if communications are carried out by using IP, it would be necessary to statically allocate as many IP addresses as the number of dial-out connection target users. In view of the current shortage of IP addresses, it is very difficult to provide the scalability to the dial-out connection. There is also a need to provide a large number of communication interfaces for use at a time of the dial-out.
In a case where a user tries to access a network, it is necessary for the user side to provide a communication device for a desired medium to be utilized by the user such as modem, adaptor for portable telephone, LAN card (Ethernet), etc., and it is also necessary for the network manager side to use communication devices for respective media. This implies that, not only the communication media that can be used by the user are going to be limited but also that there is a need for the both sides of communications to provide communication devices for respective media whenever new media are introduced so that it is difficult to deal with new media.